1. Field of the Invention
The invention relates to a method for carrying out, generally under pressure, the (notably selective) dimerization, codimerization and oligomerization reactions of olefins in the presence of at least one catalyst, usually solid, in at least one reaction zone whose temperature is controlled by a heat-exchange device with hollow plates disposed therein.
Generally, in this type of reactions, when operating in accordance with the invention, at least one of the reagents is either in the liquid state, or in a state making circulation thereof by means of a pump possible (supercritical state), such that the ratio Tr between the temperature T (in Kelvin degrees) of the reagent system and the (pseudo-) critical temperature Tc (in Kelvin degrees) of said system is preferably less than 2, for example than 1.5.
The olefin used may more particularly be chosen from ethylene, propylene, styrene, one of the isomers of the butenes or one of the mixtures thereof. This olefin may be used in the pure state or mixed with one or more compounds not reacting on the catalyst in the conditions used, such for example as cyclic or acyclic saturated hydrocarbons, in particular those having from 2 to 10 carbon atoms. The olefin concentration in the mixture may be from 5 to 100%, preferably from 10 to 100% by weight.
The invention relates more particularly to a method for the selective dimerization of propylene into methyl-4 pentene-1, for example by means of solid potassium and/or sodium based catalysts.
2. Description of the Prior Art
It is known to dimerize or oligomerize olefins in the homogeneous liquid phase so as to obtain, for example, C6 dimates (patents belonging to the Applicant U.S. Pat. No. 4,283,305 and U.S. Pat. No. 4,366,087).
It is much more difficult to carry out selective dimerization when using a heterogeneous catalyst, for example for dimerizing propylene into methyl-4 pentene-1, with sufficient selectivity, particularly greater than 85%. It is in fact then necessary to maintain a relatively constant temperature, within fairly narrow limits, below which the activity of the catalysts drops to a value which makes the reaction industrially unusable and above which consecutive isomerization reactions take place, lower the selectivity and cause practically insurmountable separation problems.
The isotherm reaction system the most often used is the single pass calender tube reactor where the inside of the tubes is filled with catalyst and thus forms the reaction medium. But, in selective dimerization, the catalytic system generally undergoes spontaneous and/or accidental (due to impurities) de-activation, which requires the periodic renewal of this catalyst, a constraint which is technically difficult to put into practice with a reactor in which the high number of tubes must be filled and emptied one by one manually.
It is also known, when the temperature of the reaction is to be maintained within relatively narrow limits to place in the catalyst bed a heat transfer apparatus either tube-based (GB No. 2,046,618), or plate-based (U.S. Pat. No. 3,666,423) or grid-based (U.S. Pat. No. 4,693,807), and to cause a fluid to flow inside this apparatus for providing heat transfer and commonly designated under the name of thermoregulation fluid.
The drawback in the use of a tube-based heat transfer apparatus is due to the fact that the connection between these individual tubes is very cumbersome and, consequently, it is very difficult to fit the assembly correctly inside the reactor. The drawback of the plate based heat transfer apparatus of U.S. Pat. No. 3,666,423 is its bulk and its low efficiency. In order to withstand the reaction pressure, the plates are only partially hollow and the thermoregulation fluid thus has only a small portion of the area of the plates for carrying out its exchange work.
In his U.S. Pat. No. 4,544,544, there has been proposed, for gas reagent systems, a method for using hollow plates, made from thin metal sheets and with rectangular internal section.
The plates used in the method of the present invention work very little under stress, which makes it possible to hollow them out completely and to let the thermoregulation fluid provide the exchange through the whole of the available area. In addition, fitting and connections are sufficiently simple so as to be readily carried out in the restricted space offered by the reactor.